oct means eight, but there are twelve notes in an octave.

is it because you'll need 8 notes to make a scale and the 1st and 8th note (1st and 13th) of a scale are the same and so it's called an octave?
still the 8th note of a scale (tonic/root) belongs to the next octave.

or is it because the greeks laid down the 'one one half one one one half' intervals for a major scale ?

first one man

8 notes in a scale, the 1st and 8th are the same note just an 'octave' apart. 8 notes apart.

you answered your own question mate =P

An octave does not have 12 semi tones in it. The 12 note scale is known as a chromatic scale and each interval between notes is a semi tone. 

An octave is called an octave, not because of how many notes is in it. It is called an octave, because the pitch of the last note in the scale is two times the (or double) the pitch of the first note in the scale. The first and last notes in the scale are also known as the "tonic" notes of the scale. 

An octave of a major scale has 2 semi tones, one between the 3rd and 4th note of the scale and one between the 7th and 8th note of the scale.  So in the key of "C", the semi tones are between the "E" and "F" notes and between the "B" and "C" notes. (Since those two intervals are half steps (semi tones), there is no such thing as an "E" sharp or "B" sharp note). 

Hope this helps.


GuitarMore.com

i just read your reply scott, i'll think about it.
i didn't know about that 2 semitone in an octave of major scale thing.

dewd, a C to an octave C does have 12 semitones between it man =P

c to c# =1
c# to d = 2
d to d# = 3
d# to e = 4
e to f = 5
f to f# = 6
f# to g = 7
g to g# = 8
g# to a = 9
a to a# = 10
a# to b = 11
b to c = 12

i don't really understand the relavence of the amount of semitones in a major scale... unless you were relating to the how many semi tones in an octave and that you were thinking in terms of the major scale rather than there is actualy 12 semi tones.

but anyway....
it is called octave for it being the 8th note in the scale that is the same note but double the frequency.
else it would make no sence for an octave higher to be called 8va on a score.

Thanks for the clarification guitarfreak on the semi tones. I knew what I was trying to say, but sure did not do a very good job explaining the point I was trying to make.

On the octave thing, a note that is one octave higher than another note has double the frequency. Middle C has a frequency of 261.63 hz. The C an octave above middle C has a frequency of 523.25 hz.

It's a great question; we are all reviewing a little music theory in our minds.

lol yeah we are =P

i didn't know that whole hz thing. might have a look at that at some point.
all i know about hz stuff is that 440 is concert pitch.

...it comes from the Latin-Italian word for EIGHT, "octavio," as in eighth-musical note:

C = 1
D = 2
E = 3
F = 4
G = 5
A = 6
B = 7
C' = 8

...and the note names came from the Greeks who used no semitones, just whole notes.

And...when western music got going, and once the semi-tones were included,  there became 13 notes to the octave, yes?

GuitarZen

Old Tele man wrote:

and the note names came from the Greeks who used no semitones, just whole notes.

OTM, didn't they use semitones for E to F and B to C in the ionian scale ?

guitarfreak wrote:

i didn't know that whole hz thing.

it's just that every note has a particular frequency and every semitone has a frequency ratio of 12th root of 2 (1.059 approx). C4 has a frequency of 264.63 hz and C#/Db has a frequency of 277.18 hz which is 264.63*277.18. it means that the notes of the chromatic scale progresses geometrically by a common ratio of 1.059.

also did you know that a note that is an octave higher than another note has twice the frequency of the lower note. and if you double the tempo of a recorded piece, it sounds an octave higher. probably increasing tape speed affects the frequency.

anybody knows a good book from which i can learn music theory ?